Single wall magnetic domain propagation arrangement

ABSTRACT

Apparatus for moving a single wall domain utilizing the finite mobility of the domain in a sheet of magnetic material is described. The domain is moved by changing pole patterns in a magnetically soft overlay in response to alternate slow and fast reversals of the in-plane field component aligned with the direction of domain movement.

United States Patent Inventor Appl. No. Filed Patented Assignee SINGLE WALL MAGNETIC DOMAIN [50] Field oi Search 340/ l 74 Primary Examiner-Bemard Konick 41mm": Examiner- Steven B. Pokotilow Attorneys-R. .l. Guenther and Kenneth B. Hamlin IELD PROPAGATION ARRANGEMENT 5 mm m ABSTRACT: Apparatus for movin a single wall domain g 0.8." 340L174 Tl, utilizing the finite mobility of the domain in a sheet of mag- 340/174 28, 340/174 CC, 340/174 MC, netic material is described. The domain is moved by changing I IMO/174 SR pole patterns in a magnetically soft overlay in response to al- .lnt. ("L Gllc 11/ 14, ternate slow and fast reversals of the in-plane field component Gl lc 19/00 aligned with the direction of domain movement.

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|2 |4 INTERROGATE 2 CIRCUIT o 1 "x I22 UTILIZATION mm PULSE FIELD souncc CIRCUIT SOURCE L3 CONTROL CIRCUIT so as BIAS F SDURCE PATENIEnIussI Ian FIG. I

7 l6 TINTERROGATE uc. d CIRCUIT SOURCE I9 R O 1 -T 32 I l I H F- IN-PLANE /22 UTILIZATION |NpUT PULSE FIELD SOURCE CIRCUIT SOURCE L K20 CONTROL CIRCUIT 36\ BIAS 35 FIELD SOURCE FIG. 2 l a 5 V 1/ TIME nvvavron A. J. KURTZ/G A T TORNE V sinctewm.

Domain propagationd'evices are well known in the art. In most" domain' prop'agation devices, a reverse magn'etized domain, having spaced-apart leading and trailing domain walls, is moved controllably in a channel structured to prevent lateral mdtiottbftl'i domain. The Bllsysti'n Technical Journal (BSTJ), volum XL'VLNo. 8 Oct. 1967, at age 1901 et seq'.; on the other hand; describes a dornain which is self bounded by a single domainwalland is free to move in the MAGNETIC DOMAIN mementos FIG. 2 isa pulse diagram of the arrangement of of FIG. I;

plane ofa sheet or slice ofniagnetic material. Movement of a domain in thelatterfcase is in responseto'an offset structured magnetic field-(gradient) which displaces the ddm'ain; in the absence of uncontrolled eitpansio'n'thereof.

- A typical'rnagnetic slice inwhich single wan domains. are

moved comprises, for example; a rare earth orthoferr'lte or a strontium or barium ferrite. A domain assumes the shape of a circle in the planeofa slice of these materials. The slices are characterized by apre'fer'red direction of magnetization normal to the slice, magneti'zation'in-a first direction along that normal beingconsidered negative and the magnetization in asecond direction' being considered positive A convenient convention is to represent a single walldomain irrsuch a slice as an encircled plus sign'whe're the circle represents the encompassing single wall of the domain. In connection with theensuing discussion; the plus sign'is omitted and the domain is represented solely as a circle. i

There are a variety of techniques for'm'oving single wall aomains. One comprises offset conduetor loops pulsed in Another technique for moving single wall domains ei'n'ploys a s'tructured magnetically soft overlay on the slice in which single wall domains are moved. Such an implementation is dis- I closed in copending application Ser. No. 732,705, filed May 28.) I968, nOW U.'S Pitt. NOL'3,534,347 for A. HJBObECk. The

overlay generatesattracting magnetic poles which move'in the overlay inresponse to 'reorienti'ng'in-plane fields. The poles at:

tract domainsalong'a predictable path determined by the overlay patterna'nd the consecutive orientations ofthe field.

This technique hasthe virtue that the overlay has no currentcarryingrequirenients and so c'an'be adap'ted for manipulating doniainsof minute size. Thetechniqiie also permits the movemerit of all domains in a sheet without discrete wiring ctmnec tidns. 1 r

BRIEF DESEIRIPTION OF THE INVENTION In accordanee with this invention, the finite mobility of a domain 'ina slice of magnetic material is turned to advantage by afield varying noniiniformly in time in, the direction of movement of a domain in the slice. In one embodiment, a sequen'ceof magnetically soft discs is aligned alongan axis adjacent asur'face'of the slice in which a domain is movetLAn illustratively constant in-plzine field is generated perpendicular to the axis. In the presence of this field, a second in-planc field in the direction of propagation'is: reversed alternately slowly and quickly. The domain follows pole patterns. inthe overlays, varying'with the In-pIane field.

FIG. 3 is an enlarged view of a portion of the arrangement of FIG. 2. I 7

DETAILED DESCRIPTION FIGQI shows a domain propagation arrangement 10 in accordance with this invention. The arrangement comprises a sheet orslice ll of magnetic materialin which a single wall domain can be moved. An overlay of magnetically soft material in the form of a sequence of spaced apart discs 12 is aligned between input and output positions shown at 13 and. 14 in FIG. 1 respectively. The discs typically comprise permalloy vapor deposited on a suitable substrate such as glass and juxtaposed'against a surface of slice 1 l. I I A representative input arrangement is shown at 13 in FIG. 1. Thearran'g'ernent includes a region R of slice. l1 outlined by a conductor 16 which is connected between a DC source 17 and ground. Source 17 provides in conductor 16 a current of a polarity to drive the outlined region R to a direction of magneti'zation of a single walldomain that is to adirection of inagnetization reversed from that of the. remainder of slice [1. A second conductor 19, of hairpin geometry, intersects a tip portionofregion R. Conductor 19 is connected between an input pulse source 20 and ground. In operation, source 20 pulses conductor-l7 to separate the tip portion into a single wall domain'for propagation. The presence of such an input pulse generates a domain which represents a binary one; the absence of a pulse results in an absent domain representing a binary zero. Information so generated is propagated along discs 12 in response to time varying in plane fields which change magnetic pole patterns in the discs ,for attracting domains in the slice therebeneath.

The propagation operation is described in detail in connection with the pulse diagram of FIG. 2 and the enlargement of a portion of arrangement 10 as shown-in FIG. 3. It is important in the illustrative embodiment that an in-plane field perpendicular to the propagation channel, as represented by arrow Hy of FIG. 1, be present for operation in accordance with this invention. Such a field may be provided by a permanent magnet or'by current-carrying coils either of which is taken to be included within the circuit represented by block 22 of FIG. I. In addition to that perpendicular field is a second in-plane fieldHx aligned along the axis-of movement of domains as viewed in FIG. I. The second field is reversed alternately at slow, than fast, rates for advancing a domain along the channel defined by the discs.

FIG. 3'shows the sequential positions occupied by a single wall domain as field Hx'is reversed. We will assume that 'a domain has been generated at 13 and moves to an adjacent disc 12. The first position for a domain is designated 1 in FIG. 3. As shown in FIG. 2, field Hx goes quickly negative as shown at l-in FIG. 2. Field Hx is large compared to field Hy; Con sequently, when Hx is quickly negative,- positive poles accumulate at the left of each disc, attracting domainsto the position l shown in FIG. 3.

Field Hx is then reversed at a relatively slow rate as indicated in FIG. 2, permitting the field Hy to generate attracting" poles for moving the domain to position 2 in FIG. 3. The

numeral designations in the pulse diagram of FIG. 2 are chosen to correspond to the position designations in FIG. 3 for convenience.

Field Hx now goes positive, to numeral 3 of FIG. 2, at the above slow rate. Again, the magnitude of field Hx is large compared to that of field Hy. Therefore, positive poles move to position 3 of FIG. 3 and the domain follows.

At this juncture in the operation, field Hx goes quickly,

negative as indicated by numeral 4 in FIG. 2. Adjacent discs l2 'as shown in FIG. 3 are sufficiently close, and changes in field from 2 to 3 of FIG. 2 sufficiently fast with respect to the mobility of the domain in slice 11 that field Hy has little effect 7 on the domain. Consequently, the domain moves to position 4.

When field Hx thereafter goes positive at the relatively slow rate, the domain moves to position 5. The terms slowly" and "quickly" herein characterize the speed of reversal of field Hx with respect to (R/pAH) where R is the radius of a disc, ais the mobility of a domain, and AH is the difference in the field due to the permalloy and acting a the leading and at the trailing edges of a domain. Typical values for slow and quick reversals are 10 microseconds and 0.1 microsecond respectively. A typical value of (R/uAH) is l microsecond for yttrium orthoferrite.

Movement ofa domain to the right along discs 12 of FIG. 1, accordingly, is achieved by alternately slow and fast reversals of the component of in-plane field aligned along the axis of domain movement in the presence of a relatively small perpendicular in-plane field component. A succession of such reversals results in the arrival of a domain at output position 14.

A representative output position comprises an overlay element typically at the terminus of a propagation channel. The element is encompassed by a conductor loop 30 connected between a utilization circuit 31 and ground. An additional conductor loop 32 also encompasses the element. Conductor 32 is connected between an interrogate circuit 33 and ground. In operation, circuit 33 pulses conductor 32 in a manner to collapse a domain in the output position. The collapse of a domain in response generates a pulse in conductor 30 for detection by utilization circuit 31.

Sources 17, 20, and 22 and circuits 3 and 33 are connected to a control circuit 35 for activation and synchronization. The various sources and circuits herein may be any such circuits capable of operating in accordance with this invention.

Overlay elements shown in FIGS. 1 and 3 are round. It is to be understood that they need not be of such geometry; oval or square geometries, for example, are adaptable in accordance with this invention. Some overlays may be employed in the absence of field Hy if they are shaped to permit a domain to move thereunder during operation, an action permitted, for example, by a nonuniform overlay.

In practice, a bias field is generally supplied for constricting domains to an ideal diameter. For materials having a preferred direction of magnetization normal to the plane of slice ll of FIG. 1, the bias field also is normal to that plane and antiparallel to the magnetization of a single wall domain. Such a field is supplied by any familiar bias field source represented by block 36 of FIG. 1. y

In one embodiment of this invention, 1 mil diameter domains are moved in a slice of a samarium terbium orthoferrite 1 mil thick in the presence of overlay elements 12 3 mils in diameter and 1,000 A thick on about 4 mil centers. In this instance, Hy is 5 oersteds and Hx has a maximum value of 15 oersteds. Alternate reversal times for H): are 10 microseconds and 0.3 microsecond. A bias field of 25 oersteds maintains a constant domain diameter. The mobility of a domain in the slice is 1,000 cm./sec. oersteds.

It should be clear from the symmetry of the overlay that a reversal of the fast and slow reversal rates as shown in FIG. 2 causes the domains to move in an opposite direction. And, of course, a reversal of the Hy and Hx field values permits a domain to be moved up and down as viewed in FIG. .1.

What has been described is considered only illustrative of the principles of this invention. Therefore, many and varied modifications can be devised by those skilled in the art in accordance with those principles still with the spirit and scope of this invention.

What is claimed is:

l. A magnetic domain propagation arrangement comprising a material in which a single wall domain can be moved and having a first surface, a magnetically soft overlay adjacent said surface, said overlay comprising a plurality of elements aligned with an axis between input and output positions, means for generating a first 1n-plane field along said axis, and

means for reversing said first in-plane field alternately at slow 7 and fast rates for advancing said domain along said axis.

. 2. An arrangement in accordance with claim I also including means for generating a second in-plane field perpendicular to said axis.

3. An arrangement in accordance with claim 2 wherein said first in-plane field is large compared to said second in-plane field.

4. An arrangement in accordance with claim 3 wherein said element is a disc and said fast rate is fast with respect to (R/pAH) where R is the radius of said disc, 5 is the mobility of a domain in said material, and AH is the difference between the field at the leading and at the trailing edges of said domain.

5. An arrangement in accordance with claim 4 where said slow rate is slow with respect to (R/,u.AH 

1. A magnetic domain propagation arrangement comprising a material in which a single wall domain can be moved and having a first surface, a magnetically soft overlay adjacent said surface, said overlay comprising a plurality of elements aligned with an axis between input and output positions, means for generating a first in-plane field along said axis, and means for reversing said first in-plane field alternately at slow and fast rates for advancing said domain along said axis.
 2. An arrangement in accordance with claim 1 also including means for generating a second in-plane field perpendicular to said axis.
 3. An arrangement in accordance with claim 2 wherein said first in-plane field is large compared to said second in-plane field.
 4. An arrangement in accordance with claim 3 wherein said element is a disc and said fast rate is fast with respect to (R/ Mu Delta H) where R is the radius of said disc, xi is the mobility of a domain in said material, and Delta H is the difference between the field at the leading and at the trailing edges of said domain.
 5. An arrangement in accordance with claim 4 where said slow rate is slow with respect to (R/ Mu Delta H). 